Field of the Invention
The present invention relates to image forming apparatuses applying an electrophotography recording technology and fixing units each attachable to an image forming apparatus.
Description of the Related Art
In some cases, one model of image forming apparatus may be designed to be usable both in a district where commercial power supply voltage is 100 V series (such as 100 V to 127 V) and in a district where it is 200 V series (such as 220 V to 240 V). An image forming apparatus applying an electrophotography recording technology may include a fixing unit configured to heat-fix an unfixed toner image formed on a recording material to the recording material. In order to allow the fixing unit to be usable in districts with different power supply voltages, a resistance value of a heater in the fixing unit may need adjustment based on the power supply voltage in each of the districts. This is because resistance values of heaters not based on power supply voltages may result in variations of amount of heat generated by the heater between the districts.
For setting a resistance value of a heater based on power supply voltage, heaters having different resistance values from each other may be mounted correspondingly in an apparatus for a 100 V district and an apparatus for a 200 V district (as in Japanese Patent Laid-Open No. 9-022224). For example, a heater having a resistance value of 10Ω may be mounted in an apparatus for a 100 V district while a heater having a resistance value of 40Ω may be mounted in an apparatus for a 200 V district. Though this method may require two types of heater, an apparatus for 100 V and an apparatus for 200 V may advantageously be manufactured at low costs.
By the way, the speeds of such image forming apparatuses have been enhanced in recent years, and some apparatuses may include a current detection function configured to detect current fed to the heater to support such increased speeds of the image forming apparatus. The current detection function may detect current fed to the heater and thus is usable for applications such as monitoring for prevention of supply of excessive power to the heater.
The ranges of values of current fed to heaters may be different between an apparatus for 100 V and an apparatus for 200 V as described above. For example, when an apparatus including a heater having a resistance value of 10Ω for 100 V is used by connecting to 100 V power supply voltage, the power consumption may be equal to 1000 W at a maximum, and the range of current values fed to the heater is equal to 0 to 10 A. When an apparatus including a heater having a resistance value of 40Ω for 200 V is used by connecting to power supply voltage 200 V, the power consumption may be equal to 1000 W at a maximum, and the range of current values fed to the heater (which will be called a heater current value) is equal to 0 to 5 A.
The ranges of heater current values in an apparatus for 100 V and the range of heater current values in an apparatus for 200 V are different. Among image forming apparatuses having a current detection function, such different ranges of heater current values may result in different resolutions of the current detection and thus result in different accuracies of the current detection between the apparatus for 100 V and the apparatus for 200 V.
Accordingly, it may be considered that an element (such as a resistance element) for prevention of such a difference in resolution for current detection between an apparatus for 100 V and an apparatus for 200 V may be attached to a main body of the apparatus for 100 V only while not attaching to a main body of the apparatus for 200 V.
However, in order to manufacture an apparatus for 100 V and an apparatus for 200 V, not only two types of fixing unit for 100 V and 200 V may be required therein, but also two types of apparatus main bodies may be required for 100 V and 200 V. This may complicate unit management during the manufacturing process and may thus increase the manufacturing costs.